Environmental and regulatory initiatives require lower levels of sulfur, nitrogen, and aromatics in distillate fuels and lubes products. For example, for distillate fuels, sulfur limits of 10–15 wppm (weight parts per million) or less have been proposed.
A major contributor to sulfur in the gasoline pool, is naphtha from fluid catalytic cracking (FCC) units. Naphtha gasoline contains high amounts of olefinic and aromatic compounds, and a relatively high amount of nitrogen and sulfur.
Some are developing technologies designed to reduce sulfur without a significant octane loss, caused by olefins saturation. Others consider hydrotreating some of the FCC naphtha to very low sulfur and nitrogen levels (<0.5 wppm) and increasing the octane number of the naphtha by reforming. This approach is of particular interest with naphthas having a relatively low octane number. Fractions to be fed to catalytic reforming need to be desulfurized before reforming because reforming catalysts are generally not tolerant to sulfur.
In U.S. Pat. No. 5,346,609 and U.S. Pat. No. 5,409,596 (Ser. No. 08/850,106), we have described a process for effectively desulfurizing catalytically cracked naphthas while maintaining a high octane number. Briefly, the process comprises an initial hydrodesulfurization step which reduces the sulfur to an acceptable level, although at the expense of octane which is restored in a subsequent step by treatment over an acidic catalyst such as one based on ZSM-5, as described in U.S. Pat. No. 5,346,609 and U.S. Pat. No. 5,490,596 (Ser. No. 08/850,106), zeolite beta as described in Ser. No. 07/891,124 (now U.S. Pat. No. 5,413,696) or MCM-22 as described in U.S. Pat. No. 5,352,354.